The present invention relates to a pneumatic tire, more particularly to a structure of a tread portion, including a tread pattern and a reinforcing cord layer, capable of improving the noise performance, steering stability and hydroplaning resistance.
Heretofore, in order to improve the hydroplaning resistance of a tire, widely employed techniques are to increase the number, widths and depths of tread grooves. Such techniques, however, involve problems with a decrease in the tread pattern rigidity, deterioration in the steering stability and deterioration in the noise performance on the dry road.
U.S. Pat. No. 7,434,606 discloses a tire provided with a tread pattern as shown in FIG. 8, wherein the tread portion (a) is divided by four circumferential grooves (b1 and b2) into a central land portion (c1), two middle land zones (c2) and two should land zones (c3). Oblique grooves (e) disposed in the middle land zones c2 are curved, gradually increasing the inclination angle θ from about zero to about 90 degrees with respect to the tire circumferential direction, toward the axially outside, and oblique grooves disposed in the should land zones (c3) are extends from the adjacent circumferential grooves (b2) to the tread edges in order to enhance the drainage. On the other hand, the axially inner ends of the oblique grooves (e) are terminated within the middle land zones (c2). The central land portion (c1) and the middle land zones (c2) extend continuously in the tire circumferential direction in order to increase the rigidity and thereby improve the steering stability. In such tire, the noise performance, steering stability and hydroplaning resistance are good, but there are rooms for improvement.